BASICS OF DESIGN ENGINEERING: FLUID POWER

The demands placed on today's fluid systems are much tougher than they were a decade ago.

Leaks that were once considered nuisances are now classified as fugitive emissions and hazardous spills, problems that can shut down plants. Modern processes are pushing pressure, flow, and temperature requirements to new heights every day, yet the basic concepts of connecting pipe have not changed much over the years. In fact, the integrity of most piping systems depends on sealing and fastening methods developed nearly a century ago.

Tubing provides one solution to tougher regulations and increasing stresses on fluid systems. Tubing and pipe both carry fluids in industrial applications, but tubing offers several advantages over pipe. Compared with pipe, tubing is generally easier to install and maintain, costs less, and performs better.

First of all, tube fittings are designed not to leak, even under rugged operating conditions because they have mechanical, metal-to-metal seals. Tightening fitting nuts coldswages ferrules onto the tubing. On the other hand, threaded-pipe connections typically require heavy equipment to cut threads and pipe dope or TFE tape to minimize leakage. In addition, the greater flexibility of tubing often means systems with fewer connections. This equates to fewer potential leak points and lower costs.

Tubing is readily available in diameters up to 2 in. with a variety of wall thicknesses and materials to meet the toughest application demands. It's important to note that tubing and pipe are sized differently. A 1-in. pipe, for instance, has a 1-in. nominal bore, while a 1-in. tube has a nominal outside diameter of 1 in.

Another advantage of tubing is that it can generally be installed faster than pipe. Tubing is cut to length and deburred, and then fittings are simply tightened onto a

Tube systems also reduce overall installed costs. Tubing is in nearly all cases less expensive to use than pipe. Although tube fittings carry a higher initial price than similarly configured pipe components, in the long run tube systems save money due to reduced downtime and simpler assembly and disassembly.

When adjustments are necessary, tubing is flexible and, thus, can be easily repositioned. This makes it possible to completely align systems before final hookup, which is especially beneficial when installing "field-routed" systems. Modifying an installed system only requires a hacksaw, wrenches, and a few new parts. And because tube connections have higher leaktight integrity than pipe connections, the systems can be reassembled easily and reliably.

Tube systems are also relatively easy to disassemble. Virtually every fitting provides a location for quick disassembly. Most fluid-handling systems are tweaked and modified on a regular basis, so quick disassembly is important. In tubing systems, users can replace an elbow with a tee in a matter of minutes, and most existing hardware can be reused. Disassembling threaded pipe, on the other hand, is more labor intensive because each component must be handled individually and sequentially. And welded pipe systems can only be disassembled by cutting, which is a lengthy process.

Tube systems also support high pressures and have, on average, a higher strength-to-weight ratio than pipe. Tubing systems produce better flow characteristics because the smooth internal surfaces reduce flow losses and drag. In addition, the internal diameters of the tubing and fittings are nearly identical, which reduces pressure drops and turbulence.

This information supplied by Swagelok Co., Solon, Ohio.

For more information, Circle 641

nut. Some tube-fitting connections can be gauged to ensure correct installation before starting up the system.

Installation of a 1-in. tubing system takes about 12 min/connection. Compare that to 1-in. Schedule-40 pipe, which requires about an hour to cut, prep, align, and weld each connection. Screwed pipe fittings require an average of 48 min to connect and align. And the cost of skilled welders and pipefitters required to install pipe systems make tubing a financially wise choice.

If welding is the only option, however, tubing and an orbital welding system can still outperform pipe. Orbital welding systems are typically quicker and simpler than manual pipe welding because fittings are designed specifically for tubing.

FLUID POWER

Handbook guides O-ring design

The Parker O-Ring Handbook is a hardcover manual with 11 chapters detailing O-ring

design. The chapters range from tutorial to purely technical in nature. For instance, technical chapters provide in-depth coverage on topics such as chemical compatibility, O-ring specifications, and sizes. The compatibility-tables chapter is actually one 53-page table listing nine common O-ring seal materials and how they react to the roughly 2,000 media listed in the table. Their compatibility is classified as satisfactory, fair, doubtful, and unsatisfactory.

More tutorial chapters include Oring elastomers, applications, and static and dynamic sealing. The chapters cover topics such as selecting the correct O-ring material, installing O-rings, the effects of friction on Orings, and avoiding O-ring failure.

One type of failure seen on reciprocating O-rings is called spiral failure. When it occurs the seal looks to be cut about halfway through the cross-section in a spiral pattern. Oddly enough, the O-ring usually seals satisfactorily until it completely breaks or separates.

Conditions that cause segments of the ring to slide and others to simultaneously roll produce spiral failure. A small amount of twisting is not detrimental. When excessive, it leads to spiral failure.

In a properly designed system, the O-ring slides during all but a small fraction of any reciprocating stroke. The seal does not normally roll or twist for several reasons. First, hydraulic pressure produces a greater holding force against the larger surface area of static components than it does against sliding surfaces.

O-rings also do not twist because running friction is lower than breakout friction so once motion begins Orings move with relative ease. Additionally, the torsional resistance of the O-ring tends to resist twisting, and the smoother finish of the sliding surface, compared to the groove

surface finish, produces less friction.

True spiral failure occurs after the seal excessively twists, but does not break, and then is subject to relatively high pressure. Fluid pressure forces the twisted seal into the sharp corner at the clearance gap. Stress above the elastomer's elastic limit then causes a rupture adjacent to the clearance gap, and slight flexing apparently causes the rupture to penetrate about halfway through the crosssection. When the O-ring is removed from the gland it returns to its original shape and the rupture appears as a tight spiral around the cross section.

According to the handbook, the three most common factors that contribute to spiral failure are low stroke speeds, lack of lubrication, and pressure differential and direction. Usually several factors combine to produce spiral failure.

One of the primary causes of spiral failure is reciprocating speeds below one fpm. At this slow speed, it appears that the sliding or running seal friction is high and comparable to breakaway friction. Extreme twisting occurs on low or balanced pressure components, such as hydraulic accumulators, in relatively few (about 200) cycles if the temperature is above 100F. O-ring seals are not recommended, therefore, for speeds less than one fpm when pressure differentials are below 400 psi. If system pressure slowly diminishes, as through slow valve leaks, and a sealed piston moves slowly through a cylinder, spiral failure is likely. The obvious remedy here is to provide good system maintenance to prevent slow leaks, or exhaust the system after each work day.

The lack of lubrication on a surface exposed to the atmosphere is another prime contributor to spiral failure,

particularly in applications with stroke lengths greater than 6 in. Remedies include using lubricated wiper rings, applying a grease that will not evaporate, lubricating metal surfaces prior to assembly, and using low-friction metal or surface plating.

Spiral failure is also more likely to occur if pressure and seal friction both act in the same direction than if they oppose each other. In other words, seals in a pump are more likely to spiral than are seals in an actuator. Normally O-rings will not twist when the pressure differential across the seal is greater than 400 psi.

Other common causes of failure are squeeze, groove shape, operating temperature, stroke length, and gland surface finish. The handbook explains these causes and recommends how to avoid them. It also points out that spiral failure is not limited to O-ring seals. Square, delta, four-leaf clover, and other cross sections can also fail by twisting. However, although other seal designs leak excessively when twisted, O-rings usually seal until they fail completely.

O-rings are stationary against gland surfaces and slide against shaft surfaces. O-rings tend not to roll in normal operation because fluid pressure forces a larger area of the O-ring against the gland than against the shaft.

Fluid pressure

Gland

Large area

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FLUID POWER

Reinventing the industrial shock absorber

Adjustable shock absorbers are widely used because they provide an economical way to decelerate loads, prevent impact damage, dampen noise, and increase equipment speeds. They're also simple to apply. One need only approximate the correct size shock from a few different models and then tune it on the machine for best performance. But ever since William J. Chorkey patented the first adjustable industrial shock absorber in 1963, there have been relatively few major innovations.

One was the introduction of self-compensating shock absorbers in the 1970s. These devices operate across a relatively wide range of input conditions without the need for adjustment. Compared with adjustable shocks, however, self-compensating units have slightly lower energy ratings and require more models to cover a given range.

Other styles were introduced over the years to accommodate specific markets, including crane bumpers, stacker-crane shocks, and soft-contact and heavy-duty units. Nonetheless, adjustable versions remain the "bread-and-butter" shocks of industrial automation.

This increasingly presents a problem for today's users. Competitive pressures demand machines that run faster and maximize throughput which, in turn, requires shocks with higher cycle rates and wider operating ranges. At the same time, there is a trend toward smaller, lighter equipment and lower costs. So simply specifying a larger shock is often not an option. Despite the fact that shock-absorber manufacturers have continuously refined their products, the nearly 40-yr-old design has nonetheless been pushed to its practical limits.

Ace Controls Inc., Farmington Hills, Mich., addressed this problem by fundamentally redesigning the basic industrial shock absorber. The resulting range of products, called the Magnum Group, features 50% more energy capacity without increasing size or cost. At the same time, Ace managed to maintain interchangeability with existing models and build in user-friendly features such as a fully threaded body, an integral stop pad, and adjustability from either end.

Designing a shock with higher energy ratings is straightforward, but it also presents sizable challenges because of a limited number of options available to increase energy-absorption capacity. In a shock, energy capacity, E, is determined by E = FS, where F = force and S = stroke. To ensure interchangeability, the stroke of each shock had to match an existing model, so designers could only manipulate force.

In the case of a shock absorber, F = PA, where P = pressure and A = area. Because existing shocks already operate at 8,000 to 12,000 psi, the best approach was to increase the piston diameter and area, rather than

pushing operating pressures beyond recommended limits.

Not surprisingly, a larger piston, inner tube, and metering tube consumed valuable space inside the shock absorber. Additional volume was lost as a direct result of the goal to create a fully threaded body, which eliminated an oversized midsection that housed the closed-cell foam accumulator.

Accumulators are a key element in shockabsorber performance. When the piston strokes, the foam accumulator collapses to accommodate the displaced oil. Typically, foam compression should be on the order of 20 to 25%.

The most expedient method to recover the lost volume was to hollow out other internal parts of the system and fill them with foam. Unfortunately, the best results with this method compressed the foam from 40 to 45%. These prototypes failed under test due to deterioration of the closed-cell foam.

Another option was to use a less-dense foam, but past experience had shown that thinner cell walls combined with high compression caused premature failures. Changing from foam to a small bladder accumulator solved the problem. While foam averages 46% solid material by volume, the bladder design, in comparison, averages only 13%. The bladder accumulator made better use of the available volume, solving the dilemma of fitting a larger piston in the same-size housing.

Energy ratings for Magnum Group shock absorbers range from 1,350 to 54,000 lb-in./cycle. This extensive range lets design engineers specify shock absorbers with higher safety factors within the same package. In some cases designers can specify smaller sizes at a lower cost. Applications include packaging machinery, conveyors, robots, and bottling equipment, or anywhere motion control is necessary.

Information for this article was provided by Mike Ferkany of ACE Controls Inc., Farmington Hills, Mich.

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ACE Magnum Group shock absorbers, which include adjustable and selfcompensating models, offer up to 3.9 times the effective weight capacity of standard models without increasing size or cost.

FLUID POWER

Give cylinder-rod contaminants the boot

Hydraulic cylinders are constantly exposed to contaminants

ranging from dust and abrasive grit to metal chips and weld spatter. Boots or bellows can protect finished rod surfaces from wear-causing elements to reduce downtime and lengthen cylinder life. A variety of designs are available in any quantity with little or no tooling charge. This lets you optimize the type of protection for your application, rather than making do with off-theshelf components.

More than one style of cover or type of material may work in an application, so the best option may not be obvious. First, consider the operating environment. Solid

contaminants such as machining chips, abrasive grinding particles, or grit can cause mechanical abrasion and wear. Fluid contaminants such as coolants, washdown water, rain, or snow require more complete sealing.

Second, look at the equipment on which the covers will be mounted. Make certain space is available for covers to fully retract and extend, and no interference points lie along the travel path. Also consider the source and volume of contaminants, and ambient and operating temperatures.

Common types of bellows include stitched, vulcanized, injection molded,

The Shurflo IRD sealless centrifugal pump from Shurflo Pump Manufacturing Co., Santa Ana, Calif., uses an axial-air-gap, brushless dc motor inside the two-chamber pump. A dividing wall is placed in the air gap, with the stator winding on one side and the rotor and impeller on the other. Energy is transmitted through the metal wall using magnetic energy created by the interaction of the stator assembly and the permanent magnet rotor. The brushless dc motor is said to produce high torque and can accept ac or dc input power.

The pump's design provides mechanical isolation to integrate the drive and control electronics next to the motor's stator assembly. Real-time measurement of fluid flow, pressure, temperature, and operating time incorporates feedback signals to create an intelligent pump. The pump can be controlled by a PLC for integration into machine-process systems.

Computer or laptop control is also possible using a serial interface and software. The pump also works in stand-alone mode with or without external sensors. A range of safety diagnostics signals is provided.

The intelligent-pump technology is suitable for demanding industrial, transportation, and marine applications. The pump features an 8-gpm flow rate at a pressure head of 7 ft. It is ignition protected and has passed all applicable UL Marine tests including UL 1331.

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FLUID POWER

and an "expanded" type. Standard stitched construction provides sufficient protection against most contaminants in moderately severe applications. The bellows have rings of elastomer-coated fabric sewn along alternate inside and outside diameters. For added protection, seams can be coated after stitching.

For more demanding conditions, vulcanized covers offer complete sealing. The covers are similar to stitched bellows, but the seams are sealed to exclude fine particles and moisture. They are also preferred where aesthetics are important. Compared with stitched construction, vulcanized covers have a lower open-toclosed-length ratio because the seams are slightly wider. This becomes critical when space is limited in retracted positions.

Injection-molded bellows offer complete sealing but present several disadvantages. For instance, mold costs are usually too high for retrofit applications. And even if stock-molded bellows are available, the material is unsupported and can tear easily. Also, the rounded convolution shapes usually provide low open-to-closed-length ratios.

Bellows-type covers expanded from a tube of fabric-reinforced elastomer are a good alternative to injection-molded bellows. They offer the same tight-sealing advantages but provide additional strength and can be made with little or no tooling charges. The bellows are cured or vulcanized after forming and feature a variety of end mountings.

Manufacturers can add many design modifications or special features to meet specific conditions. For example, cylinderrod bellows may not exhaust internal air quickly enough for high-speed cylinders. One or more screen breathers may work if the particles are not too fine. Finer contamination may require a breather hose to a clean location or an internally drilled breather hole to vent through the machine.

Other options include tie strips or tape to ensure uniform extension, and longitudinal zippers for retrofit installation. Most convoluted covers can be held in place by collars and hose clamps or flanges and backing plates.

This information supplied by A & A Manufacturing Co. Inc., New Berlin, Wis..

cylinders for their high-speed industrial labeling systems, they found that twin-rod cylinders produced faster cycle times than conventional single-rod cylinders with external guides. AZV cylinders from Hoerbiger-Origa, Glendale Heights, Ill., have two piston rods that connect to the labeling mechanisms, letting them guide the equipment without rotating. Diagraph uses the cylinders for label application and secondary wipe functions.

Speed is a major concern in labeling applications. According to Scott Rosenberger, Product Manager at Hoerbiger-Origa, compared to twin-rod cylinders, the added weight of external

guides on conventional cylinders requires more energy and time to accelerate, decelerate, and reverse directions in labeling applications.

The weight savings from using AZV cylinders lets the labeling systems apply labels faster than systems with externally guided cylinders. Labeling systems outfitted with the twin-rod cylinders apply 105 labels/min, compared to 79 labels/min for systems with externally guided cylinders. Their nonrotating motion also maintains high placement accuracy and their rugged construction provides long life with little maintenance.

This information supplied by Hoerbiger-Origa, Glendale Heights, Ill.

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FLUID POWER

VORTEX FLOWMETERS

Hydro-Flow 2300-A insertion vortex flowmeters from Fluidyne, Longmont, Colo., are made of a corrosion-resistant PVDF material. The flow-monitoring devices are used for ultrapure water, acids, and solvents. The Model 2300-A features a microprocessor-based, piezo-resistant vortex sensor with no moving parts. The sensor provides accuracy at flows of 0.3 fps with a 65:1 turndown.

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HIGH-PRESSURE NPT FLOWMETERS

The HO series of high-pressure turbine flowmeters for liquid-flow applications handles pressure ranges from 2,000 to 5,000 psi. The 316 stainless-steel flowmeters from Hoffer Flow Controls Inc., Elizabeth City, N.C., feature NPT configuration. They have a 0.2 to 800-gpm flow range and come in 0.25 to 3-in. sizes. They feature linearity 0.5% of reading over the linear flow range and repeatability of 0.1% over the usable range with a 10:1 to 100:1 turndown.

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JET-PIPE SERVOVALVES

The Moog Atchley Controls line of jet-pipe servovalves from Moog Inc., Industrial Controls Div., East Aurora, N.Y., consists of hydraulic and pneumatic servovalves, as well as pneumatic-feedback actuators. The servovalves are recommended for dirty working environments such as metalforming, wood-processing, and underwatervehicle applications. Features include a jet-pipe design to prevent fluid contamination, a single-orifice jet, high recovery pressure, and feedback wire attached to a spool. Rated flows range from 0.25 to 180 gpm at 1,000-psi valve drop. Circle 649

PLUG-IN AIR VALVE ISLAND

Solstar air-valve islands use a plug-in system of electrical connections to reduce machine downtime. The systems allow small pilot valves to be quickly assembled onto a DIN railmounted interface valve island with transparent automatic addressing up to 16 valves. Solstar valves from Parker Hannifin Corp., Pneumatic Div., Richland, Mich., are recommended for piloting process-control valves, handling vacuum, or controlling small single-acting actuators for automation. The valves have a flow rating of 0.05 Cv. Solstar valve islands are connected to a PLC with subD25, 19-pin-round, or cable-gland connectors. With IP-65 protection on electrical connections, the islands can mount close to valves and actuators in industrial environments.

and material-handling equipment, and aerospace vehicles. The software can model fuel-injection systems, engine thermal management, gearboxes, braking, power-steering, suspension systems, and valve-train dynamics. Unlike generalpurpose modeling packages, Amesim is one-dimensional, focusing on fluidpower physics and technical issues. The software has also been configured to analyze and solve hydraulic and pneumatic problems. Virtual prototypes are built and simulations run in just four steps. The software runs on Windows NT and several versions of Unix.

M5BF vane motors from Denison Hydraulics, Marysville, Ohio, are for fan-drive systems used on off-highway equipment. They have pressure ratings to 4,650 psi, speed ranges of 100 to 6,000 rpm, and a choice of five cartridges with displacements up to 2.75 cu in./rev. The motors feature replaceable cartridge assemblies with 12-vane configurations. Hydraulic pins and light springs hold the vanes radially against cam-ring contours to ensure a seal at zero speed. Radial grooves and holes balance radial hydraulic forces. Double-lip vanes are said to reduce fluid contamination.

Six families of air cylinders from Fabco-Air Inc., Gainesville, Fla., feature Teflon-lined Duralon rod bearings and chrome-plated, stainless-steel piston rods. Pancake, Square 1, and short-stroke models are available in bores from 0.5 to 4 in. with strokes to 6 in. Multi-Power cylinders come in bores from 11⁄8 to

8 in. and deliver up to 10,000 lb of thrust from a 60-psi shop-air supply.

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MANIFOLD AND SUBSYSTEM VALVES M Series manifold and subsystem valves from Valcor Scientific, Springfield, N.J., are recommended for scientific instrumentation and other industrial devices. The valves are available in a range of plastics and elastomer seal materials for application compatibility. Other options include custom electrical terminations, various mounting configurations, and custom fittings for free-standing versions.

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Dehumidifiers for industrial and commercial use

SPLIT-FLANGE ADAPTERS More than 130 new sizes and thread configurations of SAE J518 split-flange adapters are available off-the-shelf from Anchor Flange Co., Cincinnati. In addition to standard JIC thread, the line now includes SAE straight thread, O-ring face seal, and BSPP configurations. One-piece carbon-steel construction eliminates potential leak points and a compact design simplifies installation. All models also feature a corrosion-resistant zincdichromate finish. The adapters come in Code 61 and Code 62 versions, straights and angles, in sizes from 3⁄4 to

2 in. All models also include jump sizes and reducers.

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Component enhancements are reported to improve the operating efficiency of a line of desiccant dehumidifiers used by airhandler manufacturers, designbuild contractors, and building owners and managers. The DHS Series 4000 DryHandler from Air Technology Systems Inc., Desicair Div., Frederick, Md., integrates with new or existing air-handling equipment to treat humidity loads associated with process, ventilation, or make-up air. Improvements include new bearings that require no maintenance and FDA food-grade lubrication in the sealed ball bearings. An extruded dual-lipped peripheral seal prevents air from bypassing the desiccant. Two-ply, PTFE-faced air seals prevent mixing of reactivation and dehumidified air. Models range from 750 to 24,000 cfm and come in single or double-wall cabinet construction. Bypass sections for sensible air requirements handle up to 100,000 cfm. All models include the company's H-Trac capacity control, as well as reactivation energy-conservation controls.

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PNEUMATIC VACUUM PUMPS

The L Series of pneumatically driven vacuum pumps provide 13 to 32 scfm and handle high leakage rates typical in carton-handling applications. The pumps from Piab Vacuum Products, Rockland, Mass., feature an aluminum connection plate for durability and a PPS

composite body that weighs 1.43 to 1.80 lb. With only four bolts to remove, body assembly and disassembly are straightforward.

closed-center design. When matched with an accumulator, the valve supplies normal and emergency power-off braking, modulating output pressures up to 2,000 psi. Steering-assist is provided with one pedal and fullpower braking with both pedals, producing equally balanced brake pressures. The compact valves can be used in a variety of hydraulic and dual-pedal systems. The possible mounting configurations let the brake, pressure, and tank ports face up or down. A brake-light switch port for monitoring individual or balanced brake pressures and auxiliary left and right-side accumulator pressure switch ports are also available.

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New bore sizes for cylinders

Bimba Manufacturing Co., Monee, Ill., has added two bore sizes to its

Twin Bore cylinder line. The double-bore cylinders are available in 6 and 8-mm bore sizes. The smaller bores have the features of the 12 to 32-mm sizes including long piston-rod bearings for increased radial-load capacity and accurate travel, along with dual bores to exert twice the force of traditional cylinders while supplying nonrotating actuation. The Twin Bore cylinder comes in basic, double-end, and air-table models. The basic and double-end rod models include composite bushing and recirculating ball bearings. The airtable cylinder combines a rigid linear rail with recirculating ball bearings. Bumpers and retract-stroke adjustment are standard on single and doubleend models. Air-table models include external-stroke adjustment and shock absorbers for the 8-mm bore size. Circle 660

ELECTRONIC-CONTROLLED PRESSURE REGULATOR

EC8000 Series electronic-controlled pressure regulators have been added to the line of APCO valves and controls from US Para Plate Corp., Sacramento, Calif. The valves handle line pressures up to 6,000 psi with outlet pressures reaching 500 psi. They have a 316 stainless-steel construction and seal materials depend on fluid compatibility. The analog-control signal is 4 to 20 mA or 0 to 5 V. The NEMA-4 enclosure features a 0.5-in. NPT conduit connection. They regulate downstream set pressures in gas and liquid applications, as well as control pressures to high-flow, pilot-type valves.

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SINGLE-CARTRIDGE RELIEF VALVES

CR Series bidirectional relief valves are housed in a compact single cartridge and limit pressure in demanding hydraulic-control applications. The design is said to be more compact than conventional relief-valve circuits, which usually require two valves and special housing. The valves from Hydraforce Inc., Lincolnshire, Ill., come in 10-size, two- way and 08-size, three-way versions.

They feature flow rates to 16 gpm, pressures to 3,500 psi, and adjustable pressures from 200 to 3,000 psi.

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FABRIC AND WIRE- REINFORCED HOSES Fabric-reinforced hoses from Hi- Tech Hose Inc., Newburyport, Mass., feature polyester encased in thermoplastic rubber with heli- cal wire. Available in a variety of colors, the hoses resist flaking, harsh chemicals, moisture, and sunlight. Hoses come in a range of sizes from 2 to 12 in. and 25 to 50-ft lengths. They are made without glues, adhesives, or cements. Operating temperature is –40 to 275F.

Series 4000 piston accumulators for mobile-equipment applications have a 4,000-psi operating pressure and 2 to 6-in. bores with over 30 standard capacities. The 5000 piston accumulators, which are designed for rugged industrial applications, come in 2 to 9-in. bores with more than 30 standard capacities. Both series feature patented V-O-ring piston seals, serviceable threaded-end construction, and six standard seal options to handle a variety of fluids and temperatures. Circle 665

Tubing pumps

Anko Products Inc., Bradenton, Fla., offers a line of MityFlex OEM tubing pumps for a variety of applications such as mechanical lubrication, commercial warewashing and laundry equipment, and food service and retail beverage dispensing. The self-priming pumps have consistent positive displacement and handle viscosities ranging from that of air to heavy slurries. They feature speed controls with flow rates from 0.04 to 3,800 ml/min and operate on 12 or 24 Vdc or 24 to 240 V at 60 or 50 Hz.

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FLOW-RATE SENSORS

SHELL-AND-TUBE HEAT EXCHANGERS The 60 Series of sanitary shell-andtube heat exchangers from Exergy Inc., Hanson, Mass., features a 163-tube bundle in 2.5-in. shells. The 316L stainless-steel exchangers come in 10, 15, and 20-in. tube lengths and have nickel-chromium, vacuum-brazed joints. Sanitary grade fittings are used and tube-side surfaces are electropolished. The heat

exchangers meet cGMP/ANSI standards.

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FTB2000 Series Hall-effect turbine flow-rate sensors can be used for OEM applications involving low-flow liquid monitoring. The sensors from Omega Engineering, Stamford, Conn., have 0.5% repeatability and measure flow rates from 0.13 to 7.9 gpm. Turbine operation is not affected by pressure changes resulting from aging filters.

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HYDRAULIC MOTORS Type MCR low-speed/hightorque motors can be used when torque generation is required in a compact package. The motors from Mannesmann Rexroth Corp., Hydraulics Div., Wooster, Ohio, are suitable components in open or closed-loop systems. Thirty-two different displacements are available in six frame sizes. Larger sizes have the option of being switched to half displacement.

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PUSH-TO-CONNECT AIR MUFFLERS Injection-molded MMP mufflers from Mead Fluid Dynamics Inc., Chicago, reduce noise created by compressed air exiting through valves or other components. At 100 psi, for instance, noise levels can be limited to 80 dB. The push-in stem design provides easy installation and removal. The mufflers are available in 1⁄4

and 3⁄8-in., and 6 and 10-mm sizes.

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STAINLESS- STEEL CYLINDERS Stainless-steel cylinders convert pneumatic or hydraulic pressure into mechanical linear motion. The cylinders from Allenair Corp., Mineola, N.Y., are available in grades 303 or 316 with mounting hardware. They come in bore sizes from 22 to 101 mm with strokes ranging from 4 to 3,300 mm. The cylinders are available in a variety of styles including single and double ended, back to back, tandem, and multiposition. The corrosionresistant cylinders are suitable for chemical environments and washdown situations.

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CAPTIVE ACCELERATION TUBE The CAT, a captive acceleration tube from Cat Pumps, Minneapolis, is said to eliminate cavitation in pumps. Cavitation is the collapse of gaseous formations in the pumped liquid. Energy from the collapse causes erosion and pitting in pumps. The CAT stores liquid energy and kicks it into the pump as needed to assure adequate liquid to each cylinder at the beginning of its stroke. The accessory removes peaks and valleys to provide smooth, consistent inlet pressure. The pumps are 316 stainless steel and come in a range of sizes with straight and elbow adapters.

The Series from American Lewa Inc., Holliston, Mass., features the Lewa M700 pump, which requires no special start-up or operating procedures.

Full front and back-diaphragm support and a diaphragm-positioncontrol system protect against damage from cavitation and overpressure. The pump can run dry and has a built-in pressure-relief valve. The M7 diaphragm consists of two preshaped PTFE diaphragms clamped together to move as one so no intermediate fluid or vacuum coupling is needed. An integral guide creates a rolling movement without flexure. Each diaphragm serves as backup for the other. Condition monitors signal perforation of either diaphragm, while operation continues.

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FLUID-HANDLING DEVICES The OilMiser Fill-or-Drain from JLM Systems Ltd., Richmond, B.C., is a breather assembly that also allows filling and draining through a 1-in. pipe. Features include an aluminum body with two separate internal cavities, 1-in. NPT outlet port, all-weather molded plastic cap, and replaceable air filter. The mechanisms are suitable for industrial and mobile applications. A companion device mounts to 2-in. pipe bungs on standard oil drums. Fluids are transferred through portable transfer pumps, which reduces the risk of contamination and spillage.

Type 8630/31 fully integrated top control head units from Burkert Contromatic Corp., Irvine, Calif., are for decentralized, intelligent process control. With seven built-in flow patterns and the ability to design individual flow curves, internal valve trims are not required. Setpoint adjustments can be done at the valve or through standard analog input signals. A variety of direct sensor inputs can be used such as RTD, 4 to

20 mA, and frequency. Electrical interface options include ASI, Multipin, Cable Gland, Profibus, and DeviceNet. The controllers are mounted on valves and linked directly to sensors to create a local control loop. The units are recommended for applications requiring advanced levels of process automation such as textile industries, food and beverage processing, and water-treatment facilities. Stainless-steel, brass, or plastic bodies are available with different finishes and pipe connections.